Directional sound detection system



Nov. 7, 1950 R H, RANGER i 2,528,546

DIRECTIONAL SOUND DETECTION SYSTEM Filed Aug. 4, 1944 al; ACR MWQM,

. 4free/Wgr Patented Nov. 7, 1950 UNITED STATES PATENT OFFICE Newark,

Application August 4, 1944, `Serial No. 548,131

18 Claims.

(Granted under the act of March v3, 1'883, as

amended April 30, 1928; `370 0. G. 757) `The invention described v.herein may be manufactured and used by -orfor the Government for governmental purposes, without the payment of any .royalty thereon.

' This invention .relates to :sound detection and 5 more-particularly to directional sound detection devices.

. Ofthevarious devices developed in the Vpast to determine the direction of a source of sound with respect toa listener, the horn collector with its acoustic duct extended directly to .the 'listenersfearhas proved best. qualified. .Such horns presenta -large area to the wave front vand vary progressively in section exponentially from .the mouth or semi-exponentiallyto the sound conducting apparatus for the ear, so as .to create an increase 4in volume as the direction of -sound is approached.

`In `order to obtain .greaterdirectional .accuracy, 'such horns -are usually used .in pairs in order toV utilize the faculty, possessed byhuman beings `with normal hearing, known as binaural sense. `A person with Y.normal Ahearing .is able without `mechanicalaid, to turn `.sogas to face, within degreesof .azimuth thetrue direction of a source Vof sound. This .is accomplished with avbase line Aof approximately .six inches. .If .this baseline Vis increasedto a yfew feet the accuracy is greatly increased. Consequently, acoustical horns lare used in pairs-.set apart so as to. obtain abase lineof a few feet,.each horn feedingto an-ear.

Such apparatus is necessarily `bulky and cumbersome. Serious disadvantage results when portability is desired. As greater Yaccuracy is :attempted by extension, the equipment becomes more bulky. InV addition, care must be itakenfto insure'that both-horns of a pairare matched, that is, have the same acoustical properties.

"Accordingly, it is among objects Yof this invention :to providea directional sound detection device of great accuracy, high sensitivity, simple yet 'rugged construction, easy operation, and ready portability.

Another Aobject is to provide a directional sound detection device,'the operation of `which depends on newand different principles from those vheretofore known.

'.'Further objects .may beapparent .from .the iol- 2 lowing specication, claims and drawings in which:

Figure 1 shows one .form of the device as it would appear in use.

.Figure .la is a view of a .modification of the hydrogen holder.

Figure 2 illustrates the angular position of the device relativeto the direction of a sound source.

Figure 3 is a diagram for reference in describing the theory of operation.

ligurei is the approximate intensity versus degree rotation curve as the device is rotated in the vicinity of the direction to .sound source.

Figure 5 illustrates possible wave forms as -rece'ived by the ear as hereinafter explained.

.Figure X6 represents another embodiment of the principles vof this invention.

VFigures 7 and 9 are plan views of respective modifications of `the invention, and .Figure V8 is a yiront view of another modication.

.Referring now in more detailto Figure l, there is shown an approved form of the device comprising `a, cylindrical tube Ill .of metal, for instance, containing a .gas lled rubber .balloon 4ll iilled with hydrogen. One end I2 of thev hollow cylinder is closed. The other end i3 has provision for inserting the rubber gas filled balloon, after which it is closed except for a small opening I9 through which the connecting tube I4 of a listening device .such .as vstethoscope .i5 is passed. Along one side of cylinder I l there is an opening 1.6 in the form of .an elongated slot. Thus, .there is .provided asolid container with a window through which vibrations .such as sound Wavesmay pass to the surface ofan interior rilexible gas lledrcontainer, the balloon Il in this instance. l

.As an alternative, a -exible diaphragm I'l Figure 1a'(wherein .parts corresponding to those above describedhave the same reference characters, primed), such as rubber may be provided for covering slot I6. In either case -a `delicate septum is afforded between the ambient `air .and the hydrogen. The gas may then rbe introduced through valve l8.provided .at onerend of tube Il which acts -in itself as the -gas --.container. Stethoscope I5 is attached to end I9 so as to transmit sound from within the tube to the ear of -a user.

Stand -ZD-.is provided :for supporting -the equip- 3 ment in any well known way whereby tube Il is rotatable, preferably through 360 degrees.

To provide direction indication, any suitable scale 2| and pointer 22 may be attached. The adjustment of pointer 22 relative to scale 2l and tube Il is dependent on the critical angle of the tube to the incident sound path involved by the gaseous medium in the tube as hereinafter explained.

The device shown in Figure 1 `is primarily a directional sound locator and operates on the principle that sound travels faster in many mediums than it does in air. speed of sound in hydrogen is approximately three times the speed of sound in airi The application of this principle to the inven- It is known that the and steady rise as the tube is rotated toward the source of sound. A very sharp rise of several hundred percent is noted as the 191/2 degree line sweeps across the source with a sudden abrupt cut-off. Accuracy is obtained within three degrees.

The reason for such sharp characteristics is not definitely known. The following theory is offered as being the probable explanation. It should be'understood thatthe theoryadvanced is not meant to limit in anyway the scope of the invention.

y lThe time of arrival of any wave front at the tion is shown in Figure 3. The line abrepresentsl the slot I6 or diaphragm I1 in the device. cd represents the external wave front of an approaching sound in air as indicated by arrows g and h. The wave front may be assumed here as a plain wave or a straight line without material error due to the relative short length of the diaphragm Il. The external sound wave is seen to hit points c and f simultaneously. At can internal sound wave is thus initiated in the hydrogen of tube Il, which will be propagated therein as a virtual part of the original external wave, travelling a separate path, along the tube Il. It will be seen that ce is three times the distance of ef. This means then that the internal sound waveat point` c will travel along the hydrogen gas yfilled path of the diaphragm and reach point e at the same time that the original external sound wave travels through the air path from-f to e. At point e, therefore, there will be an additive push to, or increase in magnitude of, the internal wave.

This action will takeV place and progress continuously all along the path cb as the wave front continues to approach diaphragm ab. The speed at which the point of contact of the wave front with the diaphragm-travels along the diaphragm is known as the phase velocity. Point b represents the point at which the stethoscope is attached and the greatly magnified sound taken off.

It will be understood from the nature of the separating materialor septum I1 or I1. at the slot I6 that the energy of those parts of an adva'ncin'g external wave in the air which are intercepted is transferred with a minimum of reflection to the hydrogen. This being continuous throughout the length of the slot, it will be appreciated that a marked amplication of the wave front in the hydrogen is accomplished, and that departure from the critical angle will produce a relatively sharp drop of amplitude, due to phase diierence between the external and internal waves derived from the particular source which is to be located, or received. The ratio of ef to ce is the sine of the angle That ratio, when using hydrogen in the-tube il, is about 1/3, and has been found in practice to be approximately 191/2 degrees. This is then the critical angle for a hydrogen medium.

It is apparent that if the value of anglel qs is not preserved, the sound wave traveling down the hydrogen path will not reach point e at the same time that the wave following airpath approaching the diaphragm reaches point e. Thus there is no great additive push or amplification.

- Figure 4 is the curve of sound intensity versus degree rotation as experienced in actual practice. It may be seen that there is a long slow ear is a satisfactorily definite instant manifestation only when the phase and velocity of the external sound front along the diaphragm in the rair are the same as the phase and velocity of the wave within the hydrogen cell. Under these conditions the instantaneous energies imparted cumulatively through the diaphragm will strike the ear simultaneously and the front will have its original shape correspondingly amplified as it hits the ear.

As explained previously, this occurs when the wave front, assuming a plane wave, strikes the diaphragm at an angle whose sine is equal to the ratio of the velocity of sound in air to that of sound in the medium. In'the illustrated case the medium is hydrogen and the ratio is approximately l/3; the angle 19% degrees.v The direction of sound source with respect to the device is 191/2 degrees to the normal to the diaphragm.

At any lother angle withinf the 191/2-degrees, the arrival of the wave front at the ear,A instead of being instantaneous, will be distributed over a period which is equal to the longer time requiredl for one wave front to pass from the distal end to the proximal end` of the diaphragm minus the shorter time required'forthe other sound front to traverse the same parts of the diaphragm. Y

Such effects, it will be noted, may be either positive or negative. A negative value means merely that the external wave front reaches the proximal end of the diaphragmbefore it reaches the distal end, i. e. that the tube slants from the ear away from the sound source. A zero value of course means that the'wave iront coincides with, or approaches in a rdirection normal to, the diaphragm, and the energy from all portions of the wave front thus intercepted reaches the diaphragm simultaneously, and its transmission to' the ear extends over the time of transit of'sound through the length of the slot. Turning our vattention now to the harmonic components of a complex wave reaching the ldiaphragm while the latter is at the correct angular relation to the direction of the source, we see that when the period of distribution above discussed is zero the energy components from each element of the diaphragm arrive at the ear in phase and the integrated effect on the ear is that of the algebraic sum of the differential Aenergies from each element. If we assumeY that all portions ofY the diaphragm are equally effective in transmitting sound energyto the interior of the tube Il and that the wave from each linear element travels down the tube without attenuation, the instantaneous sound pressure at the proximal end `for any component of frequency f will be I l where K is a constant depending on the` length and the transmission characteristics of the diaphragmfand Po is the peak'sound pressure of the incident wave, provided the distribution time is zero, and "the contributions of each element of the diaphragm arrive in phase. If -the distribution'time is-n0t zero the-effective pressure will not be proportional'to sin 21|- jt, but to the average value of the sine function between t and t-l-tfr, where te is the distribution time. This value is y -l-.td fr sin2n'ftd! 21|ftd The eiective sound pressuretherefore becomes It will be seen that not only is this quantity inversely proportional to frequency, but that it vanishes whenY td becomes anintegral multiple oftheperiod of the component'under'consideration, fand that there is a phase displacement which is proportional to frequency.' All of these effects combine to flatten out steep wave fronts and reduce peak amplitude of complex sounds.

Departure from the critical angle by as little as halffa degree blurs speech sounds and alters both qualityand intensity of sharpreports. The degree and over all eect of the alteration depends upon the composition of the particular sound, and is diicult to show either analytically or graphically for any-general case, but it is read-v ily detected by the ear.

Thegeneral nature of the effect may be shown by considering an idealized wave consisting of a single rectangular pulse, such as is shown in Figure 5a. At the critical angle this will be heard Without distortion. With a distribution time equal to the duration of the pulse, however, the pulse would be converted, at the ear, to one of the shapes shown in Figure 5b, and with a dispersion time of twice this valueit would reach the ear asshown in Figure 5c. 1

The velocity' of propagation in themedium in the instrument, as referred to in this application, is the characteristic one listed for the material in reference works, or determined by the conventional equation based on the ratio of the modulus of elasticity to density of the medium.

It is well known that the velocity of propagation of sound varies with different materials or compositions. While hydrogen was chosen as the medium in the aboveY discussion, it is readily apparent that the principles are applicable to anyconductor of sound having a velocity of propagation'characteristic greater than that of air. Accordingly a'gas other Athan hydrogen may be used 'as the medium. Also, a liquid may be preferred to suit some occasion.` A solid block 23, illustrated in Figure 5 is suitable in replacing tube '||,r if desiredfsuccess'ful results having been obtained with both balsa wood and aluminum. Sound is taken off by attaching stethoscope H5 to one end of block 23.

The ratio of velocity ofso-und in the particular medium chosen to that in Vairrwill be the sine of the critical angle as previously explained. It is readily apparent that the value of the critical angle is immaterialso long as it is known. In the'event the velocity of sound in the chosen medium is not known, the critical angle may be quickly determined by trial, that is, taking a bearing on the known location of sound source. Scale |2| and'pointer |22 are then adjusted accordingly and the device is ready for operation.

Withtwo'tubes i I hand 2| |,arranged as shown in -Figure 7, use may be made of thewbinaural eifect. In this arrangement each tube'feeds-an ear through Ystethoscope 215. It has been "found that'a vseparation close to an angle of 180 degrees minus twice the critical angle ('180*2 in'- creases the accuracy aswell as facility Vof operation since a reversal takes place from ear to ear as the device is rotated across the sound source bearing. Y

It may be 'seen that the angle 0 of separation is somewhat arbitrary. Different effects Amay be obtained dependent on the value chosen. One effect is realized when `the angle 0 is l80-2 In the case of the hydrogen medium, angle 0 would be 141. With this Varrangement each tube of the pair reaches the critical angle and peak sound intensity simultaneously with the other as the device is rotated through the sound source bearing from either direction.

If the angle 0 is Aless than 180-2 the intensity peakV is reached in one tube before it is reached-in the other as the device is rotated through the sound source bearing. Itshou'ld be noted that this intensity rise will take'place in the tube normally feeding the ear oppositeto that one nearer the sound source. This is due to the fact that the criticalcangle is the angle between the direction `of sound source and the -normal to the longitudinal axis of the tube. To

avoid operator vconfusion with this arrangement it is suggested that 'the-corinections of the stethoscope to the tubes be reversed so that the first peak sound intensity reaches the ear nearer Yto the sound source as the device is rotated, thus creating the normal reaction of a person turning to face the sound source.

The normal effect may also be obtained by placing the tubes at an angle slightly greater than -2. In ythis way the critical angle and peak intensity is reached rst in the tube feeding the ear closer to the sound source as the device is rotated.

Further modification may be made Eby using a sound path in the shape of a cone. In this way an omnidirectional binaural effect may be obtained. The elfect is obtained in any plane having one axis intercepting the bearing line. Such afco'ne may be formed by using a plurality of tubes 3 placed within a conical support 325 as shown in Figure 8. Sound is taken from the tubes 3|| by 'tube 3|4 `culminating in mouth or opening 324 enveloping the ends 3|2 of tubes 3| Solid'bodies may be used in place of tubes 3| as previously explained, if desired.

A cone may'also be formed from the ordinary `spherical gas `filled balloon. A'suggested device so fashioned is shown in Figure 9 in which a plunger rod 24 with'curved contacting surface 25 compresses balloon 4|| against conical surface 26. Sound is taken from the apex 'M2 of the structure by mouth 424 feeding stethoscope M5.

Any Well known [form of direction indicating devices may be used inrkthese modifications.

Different conditions of use may require mechanical variations. While the fundamentals have been illustrated, it is readily apparent that a great many variations or adjustments are pos'- sible without departing from the scope of the invention.`

The stethoscope l5, ||5, 2|5, 3|5, M5, show in the several forms'of the inventionvserves as 1a transducer of the high-velocity Waves within the liquidmedium or the solid medium, to sound Waves in air having a resultant of volume or intensity Iproportionate to the accretion accomplished in the medium at I'I, 23, Ill, 3H, and so may be sensed bythe human ear. The intensity of the sound output may thus be noted. The ear pieces may be considered means for determining the intensity of sound by aural observation. Other conventional means for rendering sensible the augmented waves in the device may be employed.

I claim:

1. In a directional sound detecting system, the combination of an oblong' elastic sound transmitting body, reference means for indicating the angular position of said body, a sound conducting elastic uid medium Within said body, the characteristic velocity of propagation of sound being substantially greater` in said medium than in air, said body having a continuous linear lateral surface defining a boundary of said medium substantially parallel to its longitudinal axis exposed for continuous impact of incident sound Waves approaching lin an ambient medium in a path at an angle less than 90 degrees to said longitudinal axis, means to adjust the said body with its lateral surface at an angle to the direction of incident sound so that the component of movement of the external sound longitudinally of the body is equal to the characteristic rate of propagation of sound in said elastic fluid medium, and means for conducting sound from one end of said elastic iluid medium to an ear.

2. A directional sound detection device comprising the comibnation of an oblong rst container, a longitudinal opening or slot along at least one side of said first container, a flexible second container within said rst container, a sound conducting medium within said second container, said medium having the characteristic that the velocity of propagation of sound therein is greater than in air, means for convducting sound from said medium to an ear, and means attached to said first container for indicating the angular position of said first container.

3. A sound detection device comprising a tube having a exible longitudinal strip along at least a portion of its side, an elastic fluid sound conducting medium within said tube confined against said flexible strip and having a velocity of velope having a surface generally consonant with at least certain of said linear elements, the velocity of propagation of sound in said medium in said envelope being substantially greater than the velocity of sound in air at least, and means in communication with said medium in the envelope at a terminal location with respect to said linear elements for transducing to a sensible resultant sound waves propagated through the last-named medium.

5. In a directional sound detecting system a body having a form including linear elements of substantial length and consisting of a highly elastic sound conducting medium havinga lhigh sound propogation speed characteristic, said body having a lateral surface substantially coincident vvith certain said linear elements exposed for impact of and responsive to incident sound Waves in an ambient medium of lower sound propagation speed characteristic approaching at an oblique angle to generate sound waves in said body, means to orient the body, and transducer means located terminally With respect to said linear elements constructed to convert to a sensible form a resultant of terminal sound propagated through said body.

6. In a directional sound detection system, the combination of a formation of sound conducting substance having a major linear dimension and in which the characteristic velocity of propagation of sound is greater than in air, said formation being constructed to receive laterally along said dimension and responsively transmit with said characteristic velocity Within said substance incident sound waves in an ambient medium approaching at an angle to said dimension, means for indicating the angular position of an axis of said system, and transducer Vmeans connected with said substance responsive to terminal sound waves therein constructed to transmit a terminal resultant of sound propagated in said substance, and including means to render said resultant sensible` '7. A directional sound detection system as in claim 6 comprising a double walled container one Wall at least being a flexible concave conical sound transmitting septum of low reflective value, said substance being a fluid medium of sound conducting material in the space Within said double wall, said transducer comprising means for converting sound Waves in the material in the container adjacent the vertex of said conical surface to a sensible form.

8. In a directional sound detection system, the combination of an oblong body of sound conducting material having the characteristic that the velocity of propagation of sound therein is greater than in air and having a side exposed and elastically displaceable responsively overa major part of its principal dimension by incident sound Waves approaching in an ambient medium at a substantial angle to the major axis of the said body, means for indicating the angular position of said body, and a transducer operatively connected with a terminal part of said body constructed to transmit a resultant of sound propagated in said body, so that when said side is positioned at an incident angle to the source of sound critically related to the difference in the rates of propagation of sound in air and in said body, external soundwaves moving in ambient air and impinging on the said side will generate waves in said body, and will move in phasewith so generated waves in said body, progressively auginenting the latter Waves for determination of the optimum of said resultant. l

9. In a directional sound detection system as in claim 6, the combination of a plurality of oblong containers,Y each having said substance therein, the longitudinal axes of said containers passing through a common point, means to indicate theangular position of said'containers as a system, each said `container including a sound transmitting septum along its major dimension confining said substance, said transducer commonly connected with said substance in each said container and responsive to the terminal iripoint, means for indicating the angular position of said containers as a system, said substance being a sound conducting medium within each of said containers having boundaries exposed at said sides of the containers and regeneratively responsive to impact of sound waves in an am- Y bient medium approaching at an angle thereto toward said point, and said transducer comprising means for conducting sound terminally from each said medium within said containers.

11. A sound detection device as in claim 6 comprising in combination a plurality of elon.u gated containers constructed to admit sound Waves throughout one side and so positioned that the longitudinal axis or" each passes through a substantially common point, said substance being a sound conducting medium within each of said containers having boundaries at said sides of the containers and regeneratively responsive to incident sound waves in an ambient medium appreaching at an angle thereto toward said point, said transducer comprising means for conducting sound terminally from each said medium to an ear.

12. In a directional sound detection system as in claim 6, the combination or" a plurality of oblong bodies, the longitudinal axes of said `bodies passing through a common point, said bodies including said substance'as a sound conducting material and having lateral longitudinally extending boundaries exposed and regeneratively responsive to impact of sound Waves moving generally toward said point in a path convergent at an angle to said bodies, means to indicate the angular position of said bodies as a unit, said transducer meanscomprising means for conducting sound from one end of each of said bodies to an ear. y

13. A directional sound detecting system as in claim 6 comprising in combination a plurality of oblong bodies of said substance as sound conducting material, the longitudinal axis of each of said bodies passing through a common point, each said body having one longitudinally ex'- tending side exposed and responsive to impact of external sound waves moving in a path at an angle to the body and generally toward said point, means for indicating the angular position of said bodies as a unit, and said transducer means comprising means for conducting sound from ends of said bodies to an ear.

14. A directional sound detection system as in claim 6 comprising in combination a container comprising two concentric spaced conical suriace parts with connected base edges, at least one said surface part being a sound transmitting septum, said substance being a medium of sound conducting material Within said container between said surface parts, said transducer means being constructed for conducting terminal sound from said medium to an ear.

15. A directional sound detecting device as in .I claim 6 wherein said substance is a body of sound conducting material in the form of a concave conical surface and being of substantial thickness whereby to transmit by propagation therein Waves of compression and rarefaction of the materiai in response to impact of sound waves in a medium Within the cone, said transducer means comprising means for conducting sound from said body to an ear.

16. A sound detection system as in claim 6 comprising a container having two concentric spaced conical surface members with connected periph` eral edges, at least one of said surface members being a sound transmitting septum, said substance being conned as a sound propagating medium within said container, said transducer means being responsively combined with said substance at the vertex of the formation of said substance. Y

17. A sound Vdetection system as in claim 6, said substance comprising sound conducting elastic material of low sound Wave reecting quality in the form of a concave 'conicalsurface said transducer means comprising means for conducting a sound resultant from Within the body of said materiai at its Vertex to a remote point as a sensible resultant.

i8. A sound detecting system as in claim 6, said substance comprising a plurality of oblong formations of sound conducting material con l structed'to receive and respond to incident sound waves in an ambient medium approaching at an angle to respective longitudinal axes, the longi- VVtudinal axesof said formations radiating conically, said transducer means being connected to a terminus of each of said oblong formations.

l RICHARD I-I. RANGER. Y

REFERENCES CITED The following references are of record in the file of this patent:

UNITED s TATEs Yrnrrnrrrs 

